This section provides background information related to the present disclosure and is not necessarily prior art.
Many industries from numerous sectors of the economy have emissions of one kind or another. Such emissions can be separated into two basic groups, one being gaseous and the other being non-gaseous. It is common for emissions in the gaseous group and emissions in the non-gaseous group to contain hazardous contaminants. Emissions in the gaseous group may be in the form of exhaust gases generated by a coal fired plant or from a natural gas burning facility. Emissions in the non-gaseous group may be in the form of liquid-like, sludge-like, or slurry-like substances. If and when the level of hazardous contaminants in emissions meets and/or exceeds allowable limits, the contaminants must either be neutralized, captured, collected, removed, disposed of, and/or properly contained by one means or another.
Many industries rely upon burning a fuel material as a means to accomplish some aspect of their respective process. For instance, in a first example, steel mills burn and/or smelt metal in the process of making metal shapes, extrusions, and other metal castings. The processes used in the metal industry include operations in which particulates are emitted in metallic vapor and ionized metal. Hazardous contaminants to the environment, plants, animals, and/or humans are released into the air via the metallic vapor. To one degree or another, the hazardous contaminants in the metallic vapor and/or the metallic vapor compounds must be collected and disposed of properly. In a second example, the industry of mining precious heavy metals such as gold, silver, and platinum includes metals and metallic vapor emissions containing heavy metal contaminants and particulates that are considered hazardous if not captured, collected, and disposed of properly. In a third example, industries burning natural gas have emissions that often contain elevated levels of contaminants that are considered to be hazardous if not captured, collected, and disposed of properly. In a fourth example, the producers of energy who use coal as a burnable consumable to create steam in boilers for turning generators have considerable emissions containing metallic vapor and metallic compounds that are considered hazardous to the environment, plants, animals, and humans. Among other hazardous contaminants, metallic vapor emissions often contain mercury (Hg).
Because of the pattern of global jet streams, airborne metallic vapor emissions may be carried from one country and deposited in another. For instance, it is possible that much of the emissions of mercury generated in China and/or India may actually end up being deposited in the USA and/or the ocean waters in between. In a similar fashion, much of the mercury laden emissions generated in the USA may actually be deposited in Europe and/or in the ocean waters in between. To complete this circle, much of the mercury laden emissions generated in Europe may actually be deposited in China and/or India. Therefore, the containment of mercury and other hazardous contaminants in emissions generated by industrial processes is a global problem with global implications requiring a global effort to resolve it.
National and international regulations, rules, restrictions, fees, monitoring, and a long line of ever evolving and increasingly stringent laws are proposed and/or enforced upon those generating such emissions. The regulation and/or control over hazardous emissions varies from country to country around the world. However, it is difficult, if not impossible, for one country to enact upon another country a measure of control that endeavors to encourage, much less force, emissions producers to take measures to reduce the hazardous emissions which may be generated in that country, even though those emissions may be deposited in another country.
Japan has been a global leader in the reduction of mercury production and emissions containing mercury since the 1970s. Japan has enacted regulations which have influenced how the larger global community addresses environmental issues specifically related to mercury production. Japan's efforts to promote international mercury legislation leads the way with hopes of preventing mercury based disorders. In addition to Japan, the USA has some of the world's most stringent and restrictive laws and regulations enforced by the U.S. Environmental Protection Agency (EPA). One of the most egregious contaminants in metallic vapor emissions is mercury. The EPA has issued new and revised programs such as “Mercury and Air Toxics Standards” regulating the mercury emissions produced by various utilities across the USA with the goal of reducing the amount of mercury emitted by coal burning plants by 91% by the year 2016. Even though the imposed regulations are an ongoing subject of policy and legal debate, the over-shadowing issue remains that hazardous contaminants must be dealt with.
The jurisdiction for enforcement by the EPA does not apply to producers of hazardous emissions in industrialized nations such as India, China, Europe, and other foreign countries. Therefore, the United Nations (UN) has tried to evoke pressure upon their member nations to reduce emissions of hazardous metallic vapors. Representatives of at least 140 member nations have agreed to reduce global mercury emissions based on a treaty which took effect in 2013. However, while some global improvement has been recognized in some countries, the expansion of emerging industrialized countries seems to be greatly outpacing the improved reduction efforts.
While the primary focus on mercury does not lessen the hazardous effects of the other contaminants in the metallic vapor emissions, mercury is potentially the most prevalent and the most harmful to animals and humans. Mercury is a naturally occurring element present all over the world in plants, soil, and animals. However, human industrial processes have greatly increased the accumulation of mercury and/or mercury deposits in concentrations that are well above naturally occurring levels. On a global basis, it is estimated that the total quantity of mercury released by human-based activities is as much as 1960 metric tons per year. This figure was calculated from data analyzed in 2010. Worldwide, the largest contributors to this particular type of emission are coal burning (24%) and gold mining (37%) activities. In the USA, coal burning accounts for a higher percentage of emissions than gold mining activities.
The primary problem with exposure to mercury for animals and humans is that it is a bioaccumulation substance. Therefore, any amount of mercury ingested by fish or other animals remains in the animal (i.e. accumulates) and is passed on to humans or other animals when the former is ingested by the later. Furthermore, the mercury is never excreted from the body of the ingesting host. In the food chain, larger predators, which either live the longest and/or eat large quantities of other animals, are at the greatest risk of having excessive mercury accumulations. Humans, who eat too much mercury-laden animals, especially fish, are subject to a wide range of well-known medical issues including nervous system maladies and/or reproductive problems.
There are three primary types of mercury emissions: anthropogenic emissions, re-emission, and naturally occurring emissions. Anthropogenic emissions are mostly the result of industrial activity. Anthropogenic emission sources include industrial coal burning plants, natural gas burning facilities, cement production plants, oil refining facilities, the chloralkali industry, vinyl chloride industry, mining operations, and smelting operations. Re-emissions occur when mercury deposited in soils is re-dispersed via floods or forest fires. Mercury absorbed in soil and/or deposited in soil can be released back into the water via rain runoff and/or flooding. As such, soil erosion contributes to this problem. Forest fires, whether they are acts of nature, arson, or deliberate deforestation burning, re-emits mercury back into the air and/or water sources only to be deposited again elsewhere. Naturally occurring emissions include volcanoes and geothermal vents. It is estimated that about half of all mercury released into the atmosphere is from naturally occurring events such as volcanoes and thermal vents.
As noted above, coal burning plants release a large quantity of mercury and other contaminants into the environment each year. Accordingly, there are many ongoing efforts to reduce the amount of hazardous contaminants in the flue gas emissions produced by coal burning plants. Many coal burning plants in the USA are equipped with emissions control systems which capture, contain, and/or recover hazardous elements such as mercury. In coal burning plants, coal is burned to boil water, turning the water into steam, which is used to run electric generators. The flue gas emissions from the burning of coal are often conveyed through a conduit system to a fluid gas desulfurization unit and/or a spray dryer system, which remove some emissions and some of the noxious fumes such as sulfur dioxide (SO2) and hydrogen chloride (HCl) from the flue gases. A typical conduit system then routes the flow of flue gases to a wet or dry scrubber where more sulfur dioxide, hydrogen chloride, and fly ash are removed. The flow of flue gases is routed through a bag house where particulates are separated from the airflow in the flue gases, similar to the way a household vacuum cleaner bag works. The flue gases pass through the filter-like bags, which have a porosity allowing airflow but not the larger particulates traveling in the airflow. The surfaces of the filter bags are shaken and/or cleaned to collect the captured particulates so that they can be disposed of. Usually, these deposits are hazardous emissions themselves and must be disposed of accordingly. The balance of flue gasses that make it through this type of emissions control system is then allowed to escape through a tall smoke stack and released into the atmosphere.
The problem with this type of emissions control system is that it is virtually ineffective to capture and/or collect the heavy metals such as mercury contained in a metallic vapor and metallic compound vapor form. Since the coal fired burning systems burn coal at relatively elevated temperatures near 1,500 degrees Fahrenheit, the mercury is converted into nano-sized vapor particles that are able to slip through even the most capable filter systems. As a result, significant emissions of air borne mercury and other hazardous contaminants are released into the atmosphere.
In an effort to capture and collect mercury from coal fired systems and/or other emission sources of mercury, several known systems have been developed to address the problem, which generally fall into one of three categories.
The first category is a group of methods and/or systems that capture mercury by injecting a sorbent into the flue gas stream. Other than a noble metal, the most common sorbent material used is activated carbon, which is often halogenated with bromine. The injection of the sorbent into the flue gas is an attempt to capture contaminants in one and/or any combination of the following typical emissions control devices: an electrostatic precipitator, a fluidized gas desulfurization system, scrubber systems, or fabric filter systems. There are several variations of these systems, requiring the injection of activated carbon at various points of the emission control system after combustion of the coal. Some exemplary methods and/or systems of the first category are disclosed in U.S. Pat. Nos. 7,578,869, 7,575,629, 7,494,632, 7,306,774, 7,850,764, 7,704,920, 7,141,091, 6,905,534, 6,712,878, 6,695,894, 6,558,454, 6,451,094, 6,136,072, 7,618,603, 7,494,632, 8,747,676, 8,241,398, 8,728,974, 8,728,217, 8,721,777, 8,685,351, and 8,029,600. All of the methods and/or systems set forth in these exemplary patents generate hazardous and/or non-usable waste products, which pose their own problems for disposal. In addition, these methods and/or systems are generally not economically viable and are not capable of meeting the regulatory emissions requirements projected by the EPA and/or other global agencies.
The primary problem with the methods and/or systems of the first category of known solutions is that the use of activated carbon is expensive and inefficient. The initial expense of the activated carbon is amplified because only about 10% of the activated carbon interacts with the metallic vapor as it passes and flows through the system. Therefore, as much as 90% of expensive activated carbon is released into the flue gases as a lost expense, primarily in the form of carbon monoxide (CO) and/or carbon dioxide (CO2). Another disadvantage is that activated carbon often renders the fly ash unsuitable as a raw material for the manufacture of concrete or other industrial products requiring fillers. While the sale of fly ash is not a large income producer, in high volume quantities, this byproduct of coal burning plants does provide an additional source of income. The byproduct quantities of fly ash that are not suitable for use as filler in concrete must be classified as a hazardous waste and is therefore subject to disposal fees. On the other hand, byproduct quantities of fly ash that are suitable for use as filler in concrete are not classified as a hazardous waste and therefore are saleable product and are not subject to disposal fees.
Another problem with the methods and/or systems of the first category of known solutions is that as much as 10% of the mercury in the flue gases is not removed and is released into the environment. This percentage is high compared to the amounts of released mercury permitted by the EPA and other global agencies. As a result, none of the methods and/or systems in the first category of known solutions meet current regulations for the collection and/or capture of mercury in coal burning plants or similar industrial applications.
Yet another problem with using activated carbon is that when activated carbon is burned, carbon monoxide and/or carbon dioxide is produced and released into the atmosphere. It is estimated that as much as 2.8 billion tons of carbon dioxide is generated annually in the USA alone from the use of activated carbon in coal fired plants. Worldwide, it is estimated that there is as much as 14.4 billion tons of carbon dioxide generated annually from the burning of activated carbon in coal fired plants. In addition, activated carbon is relatively ineffective at removing mercury from other forms of non-gaseous emissions and therefore alternative methods must be applied.
The second category is a group of methods and/or systems that pretreat the coal fuel before combustion in an effort to reduce the levels of mercury in the coal fuel. Some exemplary methods and/or systems of the second category are described in U.S. Pat. Nos. 7,540,384, 7,275,644, 8,651,282, 8,523,963, 8,579,999, 8,062,410, and 7,987,613. All of the methods and/or systems set forth in these exemplary patents generate large volumes of unusable coal, which is also considered a hazardous waste. As a result, the methods and/or systems of the second category of known solutions are inefficient and expensive to operate. Furthermore, substantial capital and physical space is often required for the pretreatment of coal, making it impractical to retrofit many existing emission control systems with the necessary equipment.
The third category is a group of methods and/or systems that inject a catalyst into the emissions control equipment upstream of the activated carbon injection system. The catalyst in these methods and/or systems ionize the mercury making it easier to collect and remove the mercury from the flue gasses. However, the efficiency of such methods and/or systems is poor and operating costs are high, such that the methods and/or systems of the third category of known solutions are not cost effective. Examples of the third category of are described in U.S. Pat. Nos. 8,480,791, 8,241,398, 7,753,992, and 7,731,781. In addition to these examples, U.S. Pat. No. 7,214,254 discloses a method and apparatus for regenerating expensive sorbent materials by using a microwave and a fluid bed reactor. The method selectively vaporizes mercury from the sorbent, at which point the mercury can be caught in a specialized filter or condensed and collected. The use of microwave generation renders this method impractical for large scale commercial applications and is therefore only useful for the regeneration of expensive sorbents. Another example is found in U.S. Patent Application Publication No. 2006/0120935, which discloses a method for the removal of mercury from flue gasses using any one of several substrate materials to form chemical attractions to the mercury as the flue gasses pass through the emissions control equipment. This method is also impractical for large scale commercial use.
Therefore, current emissions control systems and methods generally operate by transferring the hazardous contaminants from a gaseous emission to a non-gaseous emission, which creates another set of emission control problems.
While many laws and regulations focus on metallic vapor emissions, other forms of emissions containing hazardous contaminants such as slurry and/or slurry-like emissions, sludge and/or sludge-like emissions, liquid and/or liquid-like emissions, and other emission variations should not be overlooked. All of the emission types listed may also require processing where the hazardous contaminants they contain can be neutralized, captured, collected, removed, disposed of, and/or properly contained by one means or another. Historically, the most cost effective and most widely used process for removing hazardous contaminants utilizes activated carbon (in one form or another), through which the emissions pass. Accordingly, the demand for activated carbon in the USA is expected to grow each year through 2017 with over one billion pounds required each and every year at a cost to industries of over $1-$1.50/pound. This equates to about $1 billion annually. Most of the projected increase in demand for activated carbon is driven by the implementation of EPA promulgated regulations, which require utilities and industrial manufacturers to upgrade coal-fired power plants to comply with ever more stringent requirements.
In addition to the ever more stringent gaseous emissions regulations, the EPA has implemented tougher regulations for non-gaseous emissions through The Clean Water Act, which must be fully complied with by 2016. The combination of increasing regulations on all types of emissions impacts multiple types of emissions that are produced by a variety of different industries. Some industries, such as electrical power producers, who burn fuel to generate power, produce primary gaseous emissions containing hazardous contaminants. Per industry standards, these gaseous emissions are exposed to activated carbon materials in an effort to capture enough volume of hazardous contaminants so as to render the gaseous emission at or below allowable limits for contaminants. The process of removing the hazardous contaminants from the gaseous emissions generated from burning these fuels results in and/or generates secondary non-gaseous emissions in the form of liquid-like or slurry-like substances containing the hazardous contaminants. The hazardous contaminants in the second non-gaseous emissions must also be captured and/or contained appropriately to prevent the hazardous contaminants from being discharged into the environment. Both the primary gaseous emissions and the secondary non-gaseous emissions require a means of properly capturing and/or reclaiming and/or confining enough of the hazardous contaminants to comply with environmental regulations. The industrial costs associated with known available processes capable of accomplishing the removal of the hazardous contaminants from the secondary non-gaseous emissions are almost so cost prohibitive that some industries are forced to shut down facilities if they cannot pass the costs along to consumers.
In accordance with some practices, non-gaseous emissions, which are considered to be hazardous because they contain elevated levels of contaminants, are consigned and contained for long-term storage in ponds, piles, or drying beds. While such practices isolate the hazardous contaminants, they are expensive and consume land area without neutralizing the hazardous contaminants themselves, which can result in environmental hazards at the containment sites. One example of a non-gaseous emission is fly ash, which is a naturally-occurring product from the combustion of coal. Fly ash is basically identical in composition to volcanic ash. Fly ash contains trace concentrations (i.e. amounts) of many heavy metals and other known hazardous and toxic contaminants including mercury, beryllium, cadmium, barium, chromium, copper, lead, molybdenum, nickel, radium, selenium, thorium, uranium, vanadium, and zinc. Some estimates suggest that as much as 10% of the coal burned in the USA consists of unburnable material, which becomes ash. As a result, the concentrations of hazardous trace elements in coal ash are as much as 10 times higher than the concentration of such elements in the original coal.
Fly ash is considered to be a pozzolan material with a long history of being used in the production of concrete because when it is mixed with calcium hydroxide a cementitious material is formed that aggregates with water and other compounds to produce a concrete mix well suited for roads, airport runways, and bridges. The fly ash produced in coal burning plants is flue-ash that is comprised of very fine particles which rise with the flue gases. Ash that does not rise is often called bottom ash. In the early days of coal burning plants, fly ash was simply released into the atmosphere. In recent decades, environmental regulations have required emission controls to be installed to prevent the release of fly ash into the atmosphere. In many plants the use of electrostatic precipitators capture the fly ash before it can reach the chimneys and exit to atmosphere. Typically the bottom ash is mixed with the captured fly ash to form what is known as coal ash. Usually, the fly ash contains higher levels of hazardous contaminants than the bottom ash, which is why mixing bottom ash with fly ash brings the proportional levels of hazardous contaminants within compliance of most standards for non-gaseous emissions. However, future standards may reclassify fly ash as a hazardous material. If fly ash is reclassified as a hazardous material it will be prevented from being utilized in the production of cement, asphalt, and many other widely used applications. It has been estimated by some studies that the cost increase of concrete in the USA alone would exceed $5 billion per year as a result of a ban on the usage of fly ash in concrete production. The increase in cost is a direct result of more expensive alternative materials being used in place of fly ash. In addition, no other known material is suitable as a direct replacement for fly ash in cement due to its unique physical properties.
Reports indicate that in the USA over 130 million tons of fly ash is produced annually by over 450 coal-fired power plants. Some reports estimate that barely 40% of this fly ash is re-used, indicating that as much as 52 million annual tons of fly ash is reused leaving as much as 78 million annual tons stored in bulk in slurry ponds and piles. Fly ash is typically stored in wet slurry ponds to minimize the potential of fugitive particulates becoming airborne, which could convey contaminants out of bulk storage and into the atmosphere and surrounding environment. In addition to airborne releases of bulk storage fly ash, there is a threat of breach and/or failure of the containment systems required for the long term containment of fly ash. One famous example of a breach occurred in 2008 in Tennessee, where an embankment of a wet storage fly ash pond collapsed, spilling 5.4 million cubic yards of fly ash. The spill damaged several homes and contaminated a nearby river. Cleanup costs are still ongoing at the time of this application and could exceed $1.2 billion.
In another example, non-gaseous emissions may be found as byproducts in typical wastewater generation systems of coal burning facilities. In typical wastewater generation systems, large volumes of water come from boiler blow down and cooling water processes. These large volumes of wastewater contain relatively low levels of contaminants and are used to dilute other waste streams containing much higher levels of contamination. The contaminated wastewater streams typically discharged from scrubber systems is diluted with the large volumes of wastewater from the boiler blow down and/or cooling water processes and then treated in large continuous mix tanks with lime to form gypsum, which is then pumped into settling ponds. During this process certain amounts of mercury and other heavy metals are entrained with the gypsum and stabilized for use in wallboard and cement. This gypsum is generally considered to be non-leaching and is not considered a pollution hazard. However, the water from the settling ponds is generally discharged into the waterways. Current regulations allow this ongoing discharge, but looming regulations propose that certain contaminants and/or levels of those contaminants be mandated as a hazardous pollution.
With regard to removing mercury and heavy metals from non-gaseous industrial wastewater streams, the use of carbonate, phosphate, or sulfide is often employed in an effort to reduce hazardous contaminants to low residual levels. One known method for removing mercury and other hazardous contaminants from industrial wastewater streams is chemical precipitation reaction. Another known method utilizes ion exchange. One of the primary problems with the chemical precipitation reaction and ion exchange methods is that these methods are not sufficient to fully comply with the ever more stringent EPA regulations for non-gaseous emissions when the amount of contaminants is high, such as for treating fly ash slurry emissions.
There are also various known commercial emissions control methods and systems sold under different tradenames for treating secondary non-gaseous emissions. One treatment method known by the tradename Blue PRO is a reactive filtration process that removes mercury from secondary non-gaseous emissions using co-precipitation and absorption. Another treatment method known by the tradename MERSORB-LW uses a granular coal based absorbent to remove mercury from secondary non-gaseous emissions by co-precipitation and absorption. Another treatment method known as Chloralkali Electrolysis Wastewater removes mercury from secondary non-gaseous emissions during the electrolytic production of chlorine. Another treatment method uses absorption kinetics and activated carbon derived from fertilizer waste to remove mercury from secondary non-gaseous emissions. Another treatment method uses a porous cellulose carrier modified with polyethyleneimine as an absorbent to remove mercury from secondary non-gaseous emissions. Another treatment method uses microorganisms in an enzymatic reduction to remove mercury from secondary non-gaseous emissions. Yet another treatment method known by the tradename MerCURxE uses chemical precipitation reactions to treat contaminated liquid-like non-gaseous emissions.